In the context of this application the term “gaseous medium” is to be understood that it covers “air” or any other gaseous medium, preferably a gaseous medium which is suitable to be used in the food industry, such as nitrogen, carbon dioxide and/or atmospheric air.
In the context of this application the term “powder material” is to be understood that it covers “powder” or any other powder material, preferably a powder material which is suitable to be used in the food industry, such as carbohydrates, proteins, stabilizers and/or emulsifiers.
Powder material intake devices and methods for taking powder material into a liquid are used for instance in the food and beverage industry in order to intake powder products into a liquid being in a process tank, especially wherein a discontinuous supply of powder material into the liquid is desired. In the process tank there is provided a low pressure or vacuum above the liquid such that a mixture of powder material and gas/air is sucked into the liquid. In some known devices the powder material is also pressurized before the powder material is supplied to the powder material intake device. These known powder material intake devices comprise a valve for opening and closing the passage through which the powder/gas mixture is sucked into the liquid in the process tank. Normally the known powder material intake devices are equipped with a single-seat valve. The single-seat valve of the powder material intake device has a wet side, i.e. the valve seat part facing the outlet of the powder material intake device (or the liquid in the process tank), and a dry side, i.e. the valve seat part facing the inlet of the powder material intake device (or the powder reservoir).
The known powder material intake devices suffer from a limited life time of the seal of the valve because there is a problem with wet powder material sticking on the seal especially when the valve is opened or closed.
When the valves opens, the low pressure or vacuum above the liquid in the process tank will create a flow of a powder gas mixture into the liquid. It is crucial that the pressure of the powder gas mixture is higher than the pressure in the process tank. Therefore a specific mass flow of the powder gas mixture will be necessary to ensure that the pressure at the dry side of the valve seat is higher than the pressure in the pressure tank. If the pressure of the powder gas mixture becomes too low, i.e. lower than the pressure in the process tank, then a backflow of wet powder or even liquid from the process tank to the valve can take place and wet also the dry side of the valve. Especially if the powder material has a high density, the powder material will queue up in front of the closed valve at the dry side thereof before opening the valve. In such cases a certain time will lapse for accelerating the powder gas mixture such that a flow of the powder gas mixture is build up which can prevent the liquid or wet powder to contact the dry side of the valve seat of the single seat valve. During the time before a sufficient flow of the powder gas mixture can be established, some backflow will take place and sometimes wet the dry side of the valve seat. These wetted areas including the valve seat and other seal areas will provide a basis for the powder to scale up and/or coat wetted areas.
When the valve closes the powder gas mixture will continue to flow between the valve seat and the closing member until the valve is fully closed and a contact between the valve seat and the closing member is reached. Therefore the powder gas mixture will be accelerated at the end of closing the valve wherein heat will be generated. This will result into abrasive wear of the seals of the valve. Furthermore the coating of the scaled up powder material on the seals and the valve seat will become very dry and hard due to the generated heat. This can finally result into a leakage through the valve.
Due to these problems the life time of the seals of the valves is sometimes only one day or a few days.